When completing an oil or gas well, there is a frequent need to penetrate or cut casing or pipe in the borehole. For example, a length of casing may be stuck in the hole, preventing retrieval. To retrieve, or salvage, the casing, a cutting tool is lowered downhole. The cutting tool contains flammable materials that are ignited and produces a flame that cuts the surrounding casing.
The initial ignition of the flammable materials is caused by an electrical initiator. The role of the initiator is to safely ignite only when intended, so as to prevent accidental, or premature, ignition, and to reliably ignite once the tool is downhole and positioned.
In the prior art, a cutting tool may use ignitors or detonators which in turn utilize resistors and black powder. The detonators are also referred to as black powder igniters or flame caps. To initiate the detonator, an electrical current is passed through the resistor, generating heat. When the resistor reaches the ignition temperature of the black powder (400-450° F.), ignition occurs. The detonator is typically placed adjacent to other flammable, or pyrotechnic materials, which are ignited.
The prior art detonators present safety concerns in that accidental detonation can occur. Consequently, the detonators require great care in their use, transporting and shipping. Furthermore, black powder performs inconsistently, depending upon various factors such as downhole conditions and even assembly of the detonator and loading the detonator into the tool. Such inconsistency adversely affects the reliability of the downhole tool.
Therefore, it is desirable to provide an ignition device that is safer and more reliable.